Enhanced-flexibility transducer arrays for delivering TTFields (tumor treating fields)

ABSTRACT

A transducer array for use in tumor-treating fields (TTFields) therapy is particularly suited for use in treating abdominal or thoracic cancers. The transducer array has features that increase its flexibility and adhesion to the patient&#39;s skin, including a branching configuration and a correspondingly branching top covering adhesive-backed layer. Additionally, a skin-level adhesive layer is provided beneath the flex circuit to which the electrode elements are attached, to help ensure thorough, lasting adhesion of the transducer array to the patient&#39;s skin over the course of treatment.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.16/698,269, filed Nov. 27, 2019, which claims the benefit of U.S.Provisional Application 62/772,867, filed Nov. 29, 2018, each of whichare incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

This application is directed to transducer arrays (i.e., arrays ofelectrode elements) used to treat cancer with tumor-treating electricfields (“TTFields therapy”). More particularly, it is directed totransducer arrays with enhanced flexibility to facilitate their use intreating, for example, thoracic or abdominal cancers.

BACKGROUND

In general, TTFields therapy is a cancer therapy that uses electricfields tuned to specific frequencies to disrupt cell division, therebyinhibiting tumor growth and causing affected cancer cells to die. WithTTFields therapy, transducers arrays are placed on opposite sides of thebody, with intimate contact between the electrodes and the patient'sskin, and an AC voltage is applied between opposing arrays at apredetermined frequency to generate the required electric fields.TTFields therapy typically continues for many months or even years,during which time the transducer arrays are replaced every 5-10 days.

In practice, the transducer arrays are provided and applied to the bodyas a unitary or self-contained unit, with the electrode elements arrayedthroughout the self-contained unit. The array of electrode elements isaffixed to the body, typically using an overlying patch with an adhesivebacking to cover the unit and hold it against the patient's skin.

Known configurations of such transducer arrays have been developed inconnection with treating Glioblastoma, in which case the transducerarrays are attached to the head. Because the skull is substantiallyrigid and immobile, good adhesion and lasting attachment of thetransducer arrays to the skin can be obtained until such time that thetransducer arrays require replacement.

On the other hand, the thoracic and abdominal regions of the body arefar more mobile than the skull is, due to general movement of the bodyand respiration. This substantially increased degree of movement cancause the transducer arrays not to adhere to thoracic and abdominalregions with the degree of intimacy of contact and/or duration ofcontact that may be desired. Higher levels of perspiration from theseareas also make it more challenging to achieve good long-term, intimateadhesion of the transducer arrays to the skin.

SUMMARY OF THE INVENTION

One aspect of the invention is directed to a first electrode apparatusconfigured for affixation to a patient's skin. The first apparatuscomprises a flex circuit having a trunk region that extends in alongitudinal direction and a plurality of branches that extend laterallyfrom the trunk region, each of the branches having a free distal end anda proximal end that is connected to the trunk region, with a pluralityof branches extending on at least one lateral side of the trunk region,the flex circuit having an inner skin-facing side and an outer side. Thefirst apparatus also comprises a plurality of electrode elementsdisposed on the inner side of the flex circuit along the branches of theflex circuit, each of the electrode elements having a conductive platethat is connected to the flex circuit in an electrically conductingmanner, and a dielectric layer positioned to face the skin of thepatient. The first apparatus also comprises a top, covering layerdisposed on the outer side of the flex circuit, the covering layer beingsized to cover the branches of the flex circuit and to overlap spacesbetween the branches, the covering layer having adhesive on askin-facing side thereof by means of which the covering layer can beadhered to the patient's skin through the spaces between the branches.The covering layer is slotted to define a plurality of fingers overlyingthe branches of the flex circuit so that the fingers of the coveringlayer can move independently of each other as branches of the flexcircuit flex independently of each other.

Some embodiments of the first apparatus further comprise a plurality ofconductive hydrogel discs, wherein each of the conductive hydrogel discsis attached to a skin-facing side of a respective electrode element.Some of these embodiments further comprise a plurality of gel barriers,wherein each of the gel barriers surrounds a respective one of thehydrogel discs.

Some embodiments of the first apparatus further comprise a foam layerdisposed on the inner side of the flex circuit, wherein the foam layeris configured to cover at least a portion of the trunk region of theflex circuit and at least a portion of the branches of the flex circuit,and leave the electrode elements uncovered. Some of these embodimentsfurther comprise a skin-level adhesive layer disposed on a skin-facingside of the foam layer. In some of these embodiments, the skin-leveladhesive layer has a configuration that follows the configuration of theflex circuit, with branches and trunk portions of the skin-leveladhesive layer being wider than corresponding portions of the flexcircuit so as to overlap spaces between the branches of the flexcircuit.

In some embodiments of the first apparatus, more electrode elements areattached to branches of the flex circuit that are closer to thelongitudinal center of the trunk than are attached to branches of theflex circuit that are farther from the longitudinal ends of the trunk.In some embodiments of the first apparatus, the trunk shifts back andforth in the lateral direction as it extends in the longitudinaldirection. In some embodiments of the first apparatus, the trunk extendsin the longitudinal direction in a straight manner.

Some embodiments of the first apparatus further comprise a skin-leveladhesive layer disposed on the inner side of the flex circuit. In someof these embodiments, the skin-level adhesive layer has a configurationthat follows the flex circuit, with branches and trunk portions of theskin-level adhesive layer being wider than corresponding portions of theflex circuit so as to overlap spaces between the branches of the flexcircuit.

Some embodiments of the first apparatus further comprise a skin-leveladhesive layer disposed on the inner side of the flex circuit, whereinthe skin-level adhesive layer is attached directly to the inner side ofthe flex circuit.

In some embodiments of the first apparatus, the flex circuit has aplurality of branches extending on each lateral side of the trunkregion. In some embodiments of the first apparatus, the flex circuit isconfigured so that no more than three paths emanate from anyintersection on the flex circuit. In some embodiments of the firstapparatus, the flex circuit is configured so that four paths emanatefrom only a single intersection on the flex circuit, and no more thanthree paths emanate from any other intersection on the flex circuit. Insome embodiments of the first apparatus, the flex circuit is configuredso that all segments of the flex circuit are straight.

Some embodiments of the first apparatus further comprise an electricalcable that terminates on the flex circuit, and segments of the flexcircuit near the distal end of each branch are thinner than at leastsome of the segments of the flex circuit that are adjacent to theelectrical cable.

Another aspect of the invention is directed to a second electrodeapparatus configured for affixation to a patient's skin. The secondapparatus comprises a flex circuit having a trunk region that extends ina longitudinal direction and a plurality of branches that extendlaterally from the trunk region, each of the branches having a freedistal end and a proximal end that is connected to the trunk region,with a plurality of branches extending on at least one lateral side ofthe trunk region, the flex circuit having an inner skin-facing side andan outer side. The second apparatus also comprises a plurality ofelectrode elements disposed on the inner side of the flex circuit alongthe branches of the flex circuit, each of the electrode elements havinga conductive plate that is connected to the flex circuit in anelectrically conducting manner, and a dielectric layer positioned toface the skin of the patient. The second apparatus also comprises a foamlayer disposed on the inner side of the flex circuit, wherein the foamlayer is configured to cover at least a portion of the trunk region ofthe flex circuit and at least a portion of the branches of the flexcircuit, and leave the electrode elements uncovered. The secondapparatus also comprises a skin-level adhesive layer disposed on askin-facing side of the foam layer. The second apparatus also comprisesa top, covering layer disposed on the outer side of the flex circuit,the covering layer being sized to cover the branches of the flex circuitand to overlap spaces between the branches, the covering layer havingadhesive on a skin-facing side thereof by means of which the coveringlayer can be adhered to the patient's skin through the spaces betweenthe branches.

Some embodiments of the second apparatus further comprise a plurality ofconductive hydrogel discs, wherein each of the conductive hydrogel discsis attached to a skin-facing side of a respective electrode element.Some of these embodiments further comprise a plurality of gel barriers,wherein each of the gel barriers surrounds a respective one of thehydrogel discs.

In some embodiments of the second apparatus, more electrode elements areattached to branches of the flex circuit that are closer to thelongitudinal center of the trunk than are attached to branches of theflex circuit that are farther from the longitudinal ends of the trunk.

In some embodiments of the second apparatus, the trunk shifts back andforth in the lateral direction as it extends in the longitudinaldirection.

In some embodiments of the second apparatus, the trunk extends in thelongitudinal direction in a straight manner.

In some embodiments of the second apparatus, the covering layer isslotted to define a plurality of fingers overlying the branches of theflex circuit so that the fingers of the covering layer can moveindependently of each other as branches of the flex circuit flexindependently of each other. In some embodiments of the secondapparatus, the flex circuit has a plurality of branches extending oneach lateral side of the trunk region. In some embodiments of the secondapparatus, the foam layer is configured to cover the entire surface ofthe flex circuit, except for regions where the electrode elements arepositioned.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of one embodiment of a transducer array thathas a first layout of electrode elements.

FIG. 2 is a plan view of the flex circuit used in the transducer arrayillustrated in FIG. 1 .

FIG. 3 is a plan view of the electrode elements used in the transducerarray illustrated in FIG. 1 .

FIG. 4 is a plan view of stiffeners used in the transducer arrayillustrated in FIG. 1 .

FIG. 5 is a plan view of conductive hydrogel discs used in thetransducer array illustrated in FIG. 1 .

FIG. 6A is a plan view of hydrogel barriers used in the transducer arrayillustrated in FIG. 1 .

FIG. 6B is a view of the hydrogel discs and hydrogel barriers as “seen”by the patient's skin.

FIG. 7A is a plan view of a skin-level adhesive layer used in thetransducer array illustrated in FIG. 1 .

FIG. 7B is a view of the hydrogel discs, hydrogel barriers, andskin-level adhesive layer as “seen” by the patient's skin.

FIG. 8A is a plan view of a foam layer used in the transducer arrayillustrated in FIG. 1 .

FIG. 8B is a view of the electrode elements and the foam layer as “seen”by the patient's skin.

FIG. 9 is a plan view of a top, covering adhesive-backed layer used inthe transducer array illustrated in FIG. 1 .

FIG. 10 is a plan view of a slot cover used in the transducer arrayillustrated in FIG. 1 .

FIG. 11 is a plan view illustrating the appearance of a transducer arrayas illustrated in FIG. 1 as applied to a patient.

FIG. 12 is a plan view of a release liner used in the transducer arrayillustrated in FIG. 1 .

FIG. 13 is an exploded view of another embodiment of a transducer arraythat has a different layout of electrode elements.

FIG. 14 is a plan view of the flex circuit of another embodiment inwhich branches are present only on a single lateral side of the trunkregion.

Various embodiments are described in detail below with reference to theaccompanying drawings, wherein like reference numerals represent likeelements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1-12 depict a first embodiment of a transducer array 100 (alsoreferred to herein as an “electrode apparatus”) with a first layout ofelectrode elements, with FIG. 1 being an exploded or assembly viewshowing all of the various components and their arrangement relative toeach other. FIGS. 2-12 show the individual components in greater detail.

One of the components that defines the configuration of the transducerarray 100 is the flex circuit 102 (FIGS. 1 and 2 ), which may be madewith electrical traces extending along the branches of the flex circuitas is well known in the art. The flex circuit 102 has a branching orramified configuration. There is a central trunk 108 a-108 g thatextends in a longitudinal direction. There are also a plurality ofbranches that extend laterally from both sides of the trunk of the flexcircuit 102. In some embodiments (including the embodiments depicted inFIGS. 1, 2, and 8 ), these branches are perpendicular to thelongitudinal direction and are arranged as rows 106 a-106 e of the flexcircuit. In the illustrated embodiment, each of the rows of the flexcircuit includes two branches—one on either side of the trunk segments108 a-108 g. The proximal end of each branch is connected to and extendsfrom the trunk of the flex circuit 102, while the distal end of eachbranch remains free. Advantageously, this configuration improves theflexibility of the flex circuit 102, and it reduces tensile stressesapplied on the transducer array 100 by skin movement (bending,stretching, twisting, breathing, etc.), thereby improving and prolongingadhesion of the array 100 to the skin. It also improves user comfort andreduces skin damage. Note that in the embodiment illustrated in FIGS. 1and 2 , the trunk 108 a-108 g shifts back and forth in segments betweensuccessive rows of the flex circuit. In these embodiments, only some ofthe segments 108 a, 108 c, 108 e, and 108 g extend in the longitudinaldirection, and those longitudinal segments are interconnected byadditional segments 108 b, 108 d, and 108 f that extend in the lateraldirection. As a result, in these embodiments, the trunk shifts back andforth in the lateral direction as it extends in the longitudinaldirection. In alternative embodiments (see, e.g., trunk 108 in the FIG.13 and FIG. 14 embodiments) the trunk is straight.

The flex circuit 102 includes a number of mounting pads 104 arrangedalong the rows 106 a-106 e.

A number of electrode elements 110 (FIGS. 1 and 3 )—for example, twentyas shown in the FIGS. 1-12 embodiment for a typically sized adultmale—are disposed on the inner (i.e., skin-facing) side of the mountingpads 104 of the flex circuit 102 (shown in FIGS. 1 and 2 ) with anelectrically conductive connection between each of the electrodeelements 110 and the flex circuit 102. The electrode elements 110 may beon the order of 1 mm thick and 2 cm in diameter and may optionally beslightly smaller in diameter than the mounting pads 104. Each of theelectrode elements 110 may be formed from a circular conductive platethat is coated with a ceramic dielectric material as is known in theart, and the circular conductor is electrically connected to anelectrical contact of the flex circuit 102. The ceramic dielectricmaterial faces toward the patient's body so it can make contact with thepatient's skin (preferably via an intervening layer of hydrogel, asdescribed below).

A corresponding number of stiffeners 112 (FIGS. 1 and 4 ) may optionallybe attached to the outer side of the mounting pads 104 of the flexcircuit 102. The stiffeners 112 may be on the order of 1 mm thick andmay be slightly smaller in diameter than the mounting pads 104. Thestiffeners 112 may be made from any suitable material (e.g., a stiff,nonconductive plastic). In general, the stiffeners 112 help prevent theelectrode elements 110 from breaking, given the flexible nature of theflex circuit 102 and the thin, fragile nature of the ceramic dielectricused for the electrode elements 110.

In some embodiments, each of the electrode elements 110 has acorresponding disc of conductive hydrogel 114 (FIGS. 1 and 5 ) disposedon the inner side of the electrode element, to establish good electricalconductivity with the patient's skin. In some embodiments, the disc ofhydrogel 114 is slightly larger in diameter than the electrode. Thematerial is preferably gamma sterilization-compatible. For example, thehydrogel discs 114 may be made from AG625, which is available fromAxelgaard, with a thickness on the order of 635 micrometers, and with avolume resistivity of 1000 ohm-cm max.

Additionally, a ring-shaped hydrogel barrier 116 (FIGS. 1, 6A, and 6B)is optionally provided, surrounding each of the hydrogel discs 114. Ingeneral, the hydrogel barriers 116 help maintain the integrity of thehydrogel 114 throughout the duration of wear and prevent migration ofthe hydrogel from its correct location under the electrode elements 110.The hydrogel barriers 116 may be made, e.g., from MED 5695R, availablefrom Vancive Medical Technologies, which is a polyethylene foam, and maybe single-coated with WetStick™ synthetic rubber adhesive, alsoavailable from Vancive Medical Technologies. The hydrogel barriers 116may be 500 micrometers thick, and are preferably gammasterilization-compatible.

To increase patient comfort, the transducer array 100 may optionallyinclude a conformal foam layer 122 (FIGS. 1, 8A, and 8B) positionedbeneath the flex circuit 102, and shaped to closely follow the branchingconfiguration of the flex circuit 102. Note that unlike the flex circuit102 (which has solid circular mounting pads 104 for the electrodeelements 110), the foam layer 122 has ring-shaped regions 124 thatsurround the electrode elements so as not to intervene between theelectrode elements 110 and the patient's skin. A suitable thickness forthe conformal foam layer 122 is on the order of 1 mm, and the foam layer122 is preferably the same thickness as the electrode elements 110. Thefoam layer 122 preferably covers the entire surface of the flexible flexcircuit 102 (except for the regions where the electrode elements 110 arepositioned) while maintaining overall flexibility and conformability ofthe transducer array 100. But in alternative embodiments, the foam layer122 only covers a portion of the surface of the flexible flex circuit102. In some embodiments, the size of the foam layer 122 may beminimized to the extent possible so as not to reduce the overallbreathability and fluid-vaporizing properties of the transducer array100.

The conformal foam layer 122 may be made, e.g., from polyethylene foamsuch as MED 5696R available from Vancive Medical Technologies. Theconformal foam layer 122 may be affixed to the flex circuit 102 using asuitable adhesive (e.g., WetStick™ synthetic rubber adhesive, alsoavailable from Vancive Medical Technologies). The foam layer 122advantageously protects the patient from potentially sharp edges of theconductive traces on the flex circuit 102. This is particularlyimportant in the context of flexible transducer arrays because flexingthe transducer arrays can cause the flat conductive traces to twist,which can cause the potentially sharp edges of those conductive tracesto tilt down towards the patient's skin. Notably, interposing the foamlayer 122 between the conductive traces of the flex circuit 102 and thepatient's skin protects the patient from cuts and/or pain that might becaused by those potentially sharp edges.

The transducer array 100 also includes a skin-level layer of adhesive118 disposed beneath the foam layer 122, as shown in FIGS. 1, 7A, and7B. (The skin-level adhesive 118 also appears in FIG. 6B.) In general,the skin-level layer of adhesive 118 follows the branching configurationof the flex circuit 102 and the foam layer 122, but with the variousbranches and trunk portions of the skin-level adhesive 118 beingslightly wider than the corresponding portions of the flex circuit 102and the foam layer 122 so as to at least partially overlap with thespaces between the branches of the flex circuit 102 and the foam layer122. Notably, the skin-level adhesive 118 includes cutouts 120 a alongthe branches of the adhesive, and cutouts 120 b at the free ends of thebranches of the adhesive. These cutouts 120 a, 120 b are shaped so asnot to intervene between the electrode elements 110 and the patient'sskin. The skin-level layer of adhesive also functions as a constructiveelement, to stabilize the central area around the electrode elements.

The skin-level layer of adhesive 118 may be made from apolyester/rayon-blend, spunlace non-woven tape material such as 3M®9917, which is 30 micrometers thick. The tape may be double-coated withacrylate adhesive, to provide a peel strength on the skin-facing side(e.g., 23 lbf/inch) and a higher peel strength (e.g., 27 lbf/inch) onthe opposite, outer side. The material is preferably hypoallergenic,highly conformable, and breathable; with a high moisture vaportransmission rate; and it is preferably gamma sterilization-compatible.To prevent excessive sweating and moisture from being trapped under thetransducer array 100, the overall surface area of the skin-level layerof adhesive 118 may be minimized, e.g., by making it just slightly widerthan the corresponding portions of the flex circuit 102 and the foamlayer 122.

Note that in embodiments where a conformal foam layer 122 is omitted,the layer of adhesive 118 would be connected directly to the flexcircuit 102 with no intervening components disposed therebetween.Alternatively, in those embodiments where the conformal foam layer 122is provided, the layer of adhesive 118 would be connected indirectly tothe flex circuit 102, with a foam layer 122 disposed therebetween.

A top, covering adhesive-backed layer 126 (FIGS. 1, 9, and 11 ) ispositioned above the outer side of the flex circuit 102. The coveringadhesive-backed layer 126 has a number of slots 128, which divide thecovering adhesive-backed layer 126 into a number of separate fingers130, each of which overlies a respective branch of the flex circuit 102.The slots 128 are preferably significantly narrower than the fingers 130and the fingers 130 are preferably wider than the diameters of theelectrode elements. This configuration results in the fingers 130 of thecovering adhesive-backed layer 126 overlapping with the spaces betweenthe branches of the flex circuit 102 to provide maximal adhesion of thecovering adhesive-backed layer 126 to the patient's skin around theelectrode elements, while still allowing the fingers 130 of the coveringadhesive layer to move independently of each other as the branches ofthe flex circuit 102 move independently of each other. This, in turn,helps to maintain conformability of the transducer array 100 andadhesion to the patient's skin even as the patient moves. In addition,the covering adhesive-backed layer 126 preferably extends beyond theperimeter of the flex circuit 102 to provide additional adhesion to theskin at the outer boundary of the transducer array 100.

The covering adhesive-backed layer 126 may be made from 3M® 9916, whichis a 100% polyester, spunlace non-woven tape. This material issingle-coated with acrylate adhesive on the skin-facing side, whichadheres the covering adhesive-backed layer 126 to the outer surface ofthe flex circuit 102, and it has a thickness of 40 micrometers. Thecovering adhesive-backed layer 126 is preferably hypoallergenic, highlyconformable, breathable, and gamma sterilization-compatible.

Notably and advantageously, two separate factors contribute to theadhesion of the entire transducer array 100 to the patient's skin. Thefirst factor is the portions of the lower surface of the top adhesivelayer 126 that contact the skin through the spaces between the branchesof the flex circuit 102 and beyond the perimeter of the flex circuit102. The second factor is the layer of adhesive 118 disposed between thefoam layer 122 and the person's skin (or, between the flex circuit 102and the person's skin in those embodiments that do not include the foamlayer 122). The inclusion of these two separate adhesive componentsprovides significantly improve adhesion of the transducer array 100 tothe patient's skin. This feature of the transducer array 100 enhancesthe degree of adhesion of the transducer array 100 to the patient's skinaround the electrode elements, resulting in prolonged and betterskin/electrode contact as compared to configurations in which the onlyadhesion was provided by an adhesive-backed patch overlying the entiretransducer array.

In some embodiments, the covering adhesive-backed layer 126 includes acentral aperture 135 and a slit 132 extending from the innermost end 129of one of the slots 128—in particular, the innermost slit-end that isclosest to the central aperture 135. The central aperture 135 permits anelectrical cable 134 (shown in FIG. 11 ) that protrudes from the backsurface of the flex circuit to extend through the coveringadhesive-backed layer 126. This electrical cable 134 is used to connectthe flex circuit 102 to a TTFields therapy controller (not illustrated)via a connector. The slit 132 is useful for positioning theadhesive-backed layer 126 over the flex circuit 102 after the cable 134has been connected to the flex circuit 102 during the assembly process.In particular, portions of the covering adhesive-backed layer 126 can bemoved away from each other to open the slit 132, such that the coveringadhesive-backed layer 126 can be passed around the electrical cable 134on either side and then the entire adhesive-backed layer can be pressedinto proper position.

Once the transducer array 100 has been properly attached to thepatient's skin with the covering adhesive-backed layer 126 securing itin place, the central aperture 135 may be covered, for protection, witha top adhesive-backed slot-cover 136 (FIGS. 1, 10, and 11 ). Theslot-cover 136 may be a disc-shaped item, formed from the same materialand in the same manner as the covering adhesive-backed layer 126. Insome preferred embodiments, the slot cover 136 includes a slot 138 forthe electric cable 134 to pass through.

In some preferred embodiments, the entire assembly of componentsdescribed above is protected, prior to use on a patient, with a two-partrelease liner 140 (FIGS. 1 and 12 ). The release liner has an overallshape that generally follows, but may be slightly larger than, the outerperiphery of the covering adhesive-backed layer 126. It may be madee.g., from AR W4000, available from Adhesive Research, which is a white,silicone-coated PET (polyethylene terephthalate) material that is 50micrometers thick.

In the FIGS. 1-12 embodiment of a transducer array 100 described above,there are 20 electrode elements arranged in five rows, with two, five,six, five, and two electrode elements in each of the successive rows.(The rows correspond with the branches of the flex circuit and areperpendicular to the longitudinal direction in which the trunk extends.Thus, the rows are oriented horizontally and the trunk is orientedvertically as the transducer array 100 is oriented in FIG. 1 and theflex circuit 102 is oriented in FIG. 2 .) Depending on factors such asthe size, sex, age, etc. of a patient, however, there could be more orless electrode elements arranged in different configurations, whilestill adhering to the inventive concepts disclosed herein. For example,as illustrated in FIG. 13 , there could be 13 electrode elementsarranged in five rows (rows oriented vertically in FIG. 13 ), with therebeing two, three, three, three, and two electrode elements in successiverows and with the rows being interconnected by a trunk 108 of thetransducer array that extends in a straight line all the way across thedevice (trunk oriented horizontally in FIG. 13 ). Furthermore, in bothillustrated embodiments, there are more electrode elements in the rowsthat are closer to the longitudinal center of the trunk than there arein the rows that are closer to the longitudinal ends of the trunk. Inother embodiments (not illustrated), there could be the same number ofelectrode elements in all rows, i.e., along all branches of the flexcircuit.

In both the FIGS. 1-12 embodiment and the FIG. 13 embodiment, the flexcircuit 102 has a plurality of branches extending on each lateral sideof the trunk region. But in alternative embodiments, the branches may bepresent only on a single lateral side of the trunk region (in whichcase, the trunk region would be located near one edge of the apparatus.

FIG. 14 depicts an example of a configuration in which the branches arepresent only on a single lateral side of the trunk region. In thisembodiment, the flex circuit 102 has a linear trunk 108, a plurality ofbranches 106 a-106 d, and a plurality of mounting pads 104 a-104 cpositioned on those branches. The remaining elements in this embodimentsuch as the stiffeners, the electrode elements, the foam layer, thehydrogel, the hydrogel barrier, the skin layer adhesive, the topcovering adhesive backed layer, the electrical cable, and the slotcover, etc. (not shown) are similar to the corresponding elements in theFIG. 1-12 embodiment, except that the positioning of those elementsfollows the structure of the FIG. 14 layout as opposed to the structureof the FIG. 2 layout. As explained above in connection with the FIG. 2embodiment, positioned above the outer side of the flex circuit 102 isan adhesive-backed layer that has a number of slots. These slots dividethe covering adhesive-backed layer into a number of separate fingers,each of which overlies a respective branch of the flex circuit 102. Thisconfiguration allows the fingers of the covering adhesive layer to moveindependently of each other as the branches of the flex circuit 102 moveindependently of each other. This, in turn, helps to maintainflexibility and conformability of the transducer array and adhesion tothe patient's skin even as the patient moves.

In some embodiments (including but not limited to the FIGS. 1-12embodiment) the flex circuit is configured so that no more than threepaths emanate from any given intersection on the flex circuit. This isbest explained in connection with FIG. 2 , from which it is apparentthat one path of the flex circuit emanates from the intersections at themounting pads 104 a, two paths of the flex circuit emanate from theintersections at the mounting pads 104 b, and three paths of the flexcircuit emanate from the intersections at the mounting pads 104 c.Notably, there are no intersections on the flex circuit 102 from whichmore than three paths emanate. This holds true for both theintersections that are positioned at the mounting pads 104, and also forintersections that are not positioned at one of the mounting pads 104(e.g., The T-shaped intersections 105). The FIG. 14 embodiment similarlyhas no intersections on the flex circuit 102 from which more than threepaths emanate. Configuring the flex circuit 102 so that there are nointersections from which more than three paths emanate (e.g., asdepicted in FIGS. 2 and 14 ) improves the flexibility of the flexcircuit, which advantageously improves the flexibility of the entireapparatus.

In alternative embodiments (e.g., the FIG. 13 embodiment), intersectionsdo exist from which four paths emanate (see, e.g., the three mountingpads in the center of the apparatus). In other alternative embodiments(not shown) only a single intersection exists from which four pathsemanate.

In some preferred embodiments, including the FIGS. 1-12 and FIG. 13embodiments, all segments of the flex circuit are straight.

In some preferred embodiments, including the FIGS. 1-12 and FIG. 13embodiments, an electrical cable terminates on the flex circuit (as bestseen in FIG. 11 ). Optionally, in these embodiments, (as best seen inFIG. 2 ) segments of the flex circuit 102 near the distal end of eachbranch are thinner than at least some of the segments of the flexcircuit 102 that are adjacent to the location where the electrical cableterminates (e.g., segment 108 d). This configuration increases theflexibility of the flex circuit, which also contributes to improving theflexibility of the entire apparatus.

While the present invention has been disclosed with reference to certainembodiments, numerous modifications, alterations, and changes to thedescribed embodiments are possible without departing from the sphere andscope of the present invention, as defined in the appended claims.Accordingly, it is intended that the present invention not be limited tothe described embodiments, but that it has the full scope defined by thelanguage of the following claims, and equivalents thereof.

What is claimed is:
 1. An electrode apparatus configured for affixationto a patient's skin, comprising: a flex circuit having a trunk regionthat extends in a longitudinal direction and a plurality of branchesthat extend laterally from the trunk region, each of the branches havinga free distal end and a proximal end that is connected to the trunkregion, with a plurality of branches extending on at least one lateralside of the trunk region, the flex circuit having an inner skin-facingside and an outer side; a plurality of electrode elements disposed onthe inner side of the flex circuit along the branches of the flexcircuit, each of the electrode elements having a conductive plate thatis connected to the flex circuit in an electrically conducting manner,and a dielectric layer positioned and adapted to be facing the skin ofthe patient; a foam layer disposed on the inner side of the flexcircuit, wherein the foam layer is configured to cover at least aportion of the trunk region of the flex circuit and at least a portionof the branches of the flex circuit, and leave the electrode elementsuncovered; a skin-level adhesive layer disposed on a skin-facing side ofthe foam layer; and a top, covering layer disposed on the outer side ofthe flex circuit, the covering layer being sized to cover the branchesof the flex circuit and to overlap spaces between the branches, thecovering layer having adhesive on a skin-facing side thereof by means ofwhich the covering layer can be adhered to an underlying surface throughthe spaces between the branches.
 2. The electrode apparatus of claim 1,further comprising a plurality of conductive hydrogel discs wherein eachof the conductive hydrogel discs is attached to a skin-facing side of arespective electrode element.
 3. The electrode apparatus of claim 1,wherein the covering layer is slotted to define a plurality of fingersoverlying the branches of the flex circuit so that the fingers of thecovering layer can move independently of each other as branches of theflex circuit flex independently of each other.
 4. The electrodeapparatus of claim 1, wherein the flex circuit has a plurality ofbranches extending on each lateral side of the trunk region.
 5. Theelectrode apparatus of claim 1, wherein the foam layer is configured tocover the entire surface of the flex circuit, except for regions wherethe electrode elements are positioned.
 6. The electrode apparatus ofclaim 2, further comprising a plurality of gel barriers, wherein each ofthe gel barriers surrounds a respective one of the hydrogel discs. 7.The electrode apparatus of claim 1, wherein more electrode elements areattached to branches of the flex circuit that are closer to thelongitudinal center of the trunk than are attached to branches of theflex circuit that are closer to the longitudinal ends of the trunk. 8.The electrode apparatus of claim 1, wherein the trunk shifts back andforth in the lateral direction as it extends in the longitudinaldirection.
 9. The electrode apparatus of claim 1, wherein the trunkextends in the longitudinal direction in a straight manner.
 10. Theelectrode apparatus of claim 1, wherein the skin-level adhesive layerhas a configuration that follows the configuration of the flex circuit,with branches and trunk portions of the skin-level adhesive layer beingwider than corresponding portions of the flex circuit so as to overlapspaces between the branches of the flex circuit.
 11. The electrodeapparatus of claim 1, wherein the flex circuit has a plurality ofbranches which are present only on a single lateral side of the trunkregion.
 12. The electrode apparatus of claim 1, wherein the flex circuitis configured so that no more than three paths emanate from anyintersection on the flex circuit.
 13. The electrode apparatus of claim1, wherein the flex circuit is configured so that one or moreintersections on the flex circuit exist from which four paths emanate.14. The electrode apparatus of claim 1, wherein the flex circuit isconfigured so that all segments of the flex circuit are straight. 15.The electrode apparatus of claim 1, further comprising an electricalcable that terminates on the flex circuit.
 16. The electrode apparatusof claim 15, wherein segments of the flex circuit near the distal end ofeach branch are thinner than at least some of the segments of the flexcircuit that are adjacent to the electrical cable.